A conventional amorphous silicon solar cell system comprises a plurality of unit solar cells that are formed by superposing transparent electrodes, amorphous silicon (a-Si) film regions and back electrodes on a single glass substrate. The individual unit solar cells are connected in series in such a manner that the back electrode of one unit cell contacts the transparent electrode of an adjacent unit cell via a conductive path.
Solar cells are inherently designed to utilize the electric energy directly converted from sunlight and no considerations have been made to adapt solar cells to applications that have nothing to do with this photovoltaic conversion of sunlight to electricity. Since conventional solar cells use tin oxide or indium-tin oxide in transparent electrodes, their reflectance is too low to enable use as mirrors (for the reflectance of SnO.sub.2 as compared to metals, see FIG. 2).
Another problem with the prior art is the difficulty involved in attempts at reducing the cost of materials. Currently, thin films of tin oxide or indiumtin oxide are deposited by a thermal CVD process or sputtering but this requires the use of not only expensive oxide targets but also a complicated sputtering apparatus such as one using a radio-frequency magnetron.